1. Field of the Invention
This invention relates to reinforcement structures and methods, and in particular to a reinforcement structure and method for a subterranean masonry block wall.
2. Description of the Prior Art
Walls constructed of masonary blocks are well known in the field of construction and have been extensively used for both above ground and subterranean walls. Such masonary block construction offers the advantage of being relatively inexpensive and walls constructed in this manner are generally capable of supporting residential and light commercial structures thereon.
The blocks generally have two or more passages extending therethrough and, when a wall is constructed, the respective passages of blocks superposed on each other are generally aligned vertically. Although it is known to secure steel reinforcing bars in such aligned passages when a wall is constructed, this practice is frequently omitted as a cost expedient. Therefore, many structures in existence today have subterranean walls comprising unreinforced masonry blocks. Also, building codes in some jurisdictions still allow the construction of such unreinforced subterranean masonry block walls, rather than requiring that such walls be constructed of poured concrete, which is inherently stronger and more resistant to lateral loads associated with, for example, the soil surrounding such subterranean walls.
Although such masonry block walls may have sufficient strength to support structures placed thereon and to carry the downward forces associated therewith, they are inherently weak in lateral loads. Unreinforced subterranean masonry walls are therefore particularly susceptible to cracking from the pressures associated with the surrounding soil. Such pressure may be caused by a horizontal force component associated with the weight of the surrounding soil. Also, such lateral forces may be caused by expansion of the surrounding soil. Partially saturated soil is known to expand when the moisture content thereof is raised. Such expansion occurs in various amounts depending upon the elasticity of the particular soil. When drought conditions occur, soil shrinkage causes surface cracks which allow deep penetration of subsequent precipitation. Water penetrating deeply into soil adjacent a subterranean wall causes substantial lateral movement of the expanding soil against the wall.
Over a period of time, unreinforced masonry block subterranean walls frequently develop diagonal cracks at the ends thereof and vertical cracks near their centers. Such cracks can admit water under pressure from the surrounding soil and, if left untreated, can progressively widen and eventually precipitate the collapse of the entire foundation with resultant damage to the structure supported thereon. In addition to developing such cracks, subterranean unreinforced masonry walls typically either bow inwardly or, if not sufficiently attached to an overlying floor structure, pull inwardly therefrom and tilt. As such bowing or tilting steadily worsens with cycles of drought and precipitation, the weight of the overlying structure tends to exert ever increasing buckling forces against such a wall.
This inherent weakness of unreinforced masonry block walls when subjected to lateral pressure, is attributable to the structural characteristics of the masonry blocks themselves and the mortar joints at which they are connected. Walls constructed in this manner are relatively strong in compression and are thus well suited for supporting overlying structures thereon. However, the mortar joints are weak in tension, and when adjacent blocks are subjected to a tensile force, they tend to separate relatively easily. Lateral forces resulting from, for example, the expansion of surrounding soil, exert a bending moment against the wall which includes a compressive force component at the outer face and a tensile force component at the inner face. Basement wall cracks therefore tend to develop on the insides of such walls as they are either bowed or tilted inwardly.
One method of dealing with such cracked and deformed subterranean walls is shown in the Hevner U.S. Pat. No. 377,940 wherein jacks are utilized for straightening a wall and wedges are placed in buckled portions of the wall to redistribute the compressive forces thereat. Another method for dealing with cracks in masonry walls is shown in the Walter U.S. Pat. No. 2,417,026 and involves the placement of a yieldable and expandable filling material in the cracks. Although such filling material may deter the admission of water therethrough, the individual masonry units are not bound together thereby sufficiently to resist additional separation.
The Johnson et al U.S. Pat. No. 4,189,891 discloses a method for anchoring and straightening subterranean walls including the steps of digging a hole in the earth a distance from the wall to be repaired, inserting a threaded shaft through the wall and the surrounding earth and into the hole where it is secured with concrete. The threaded shaft is tightened by means of a nut positioned inside the basement wall and engaging a plate thereat whereby the wall is drawn outwardly to a straightened position and anchored.
Yet another method involves the placement of steel reinforcing columns against the inside face of the basement wall. Finally, the overlying structure may be supported on jacks while the surrounding earth is excavated and the cracked and deformed basement wall removed and replaced, although this method frequently necessitates the destruction of landscaping adjacent the structure.
Such prior art methods and structures for reinforcing subterranean masonry walls have typically been relatively complex to construct or use, necessitating a relatively high cost to execute, or have been relatively ineffective at sufficiently strengthening such walls to effectively resist the lateral loads exerted thereagainst by the surrounding soil.